1. Field of the Invention
The present invention relates to an antenna; in particular, to current breakers of antenna structures and wireless communication devices having the same.
2. Description of Related Art
In general microwave circuits, electrical current flows along the edge of the ground plane of a substrate, resulting in additional radiation that interferes with the original characteristics of an antenna. Related designs of a current breaker were therefore incorporated in today's communication products, however, with a lack of practicality due to the need of a large area.
Reference is made to FIG. 1. FIG. 1 is a schematic view showing a traditional one quarter wavelength current breaker, and the proposed method is related to a traditional current breaker with one quarter wavelength. Please refer to the reference: Peter Lindberg and Erik Öjefors, “A Bandwidth Enhancement Technique for Mobile Handset Antennas Using Wavetraps,” IEEE Transactions on Antennas and Propagation, vol. 54, No. 8, pp. 2226-2233, August 2006. The antenna 11 is arranged on top of the ground plane 10 as shown in FIG. 1 and the portion of the slash area is the projection of the antenna 11 on the substrate. In conventional designs, the ground plane 10 features the quarter-wavelength-resonance current distribution of the antenna 11. The design of adding the current breaker 12 to the end edge of the ground plane 10, or appropriately placing the current breaker 12 on the ground plane 10 could reduce the higher order resonance frequency originally provided by the ground plane 10, thereby increasing the original impedance bandwidth of the antenna 11. The main purpose of this design is to decrease by means of the current breaker 12 the higher order resonance frequency provided by the ground plane 10, so as to let the antenna operate in a broad bandwidth. However, in this manner it is unpractical and less useful since the component size of the current breaker 12 is roughly equal to quarter wavelength corresponding to the operation frequency, resulting in the need of a large area.
Reference is made to FIG. 2. FIG. 2 is another embodiment of the current breaker of prior art. Please refer to Reference: Chi-Yuk Chiu, Chi-Ho Cheng, Ross D. Murch and Corbett. R. Rowell, “Reduction of Mutual Coupling Between Close-Packed Antenna Elements, “IEEE Transactions on Antennas and Propagation, vol. 55, No. 8, pp. 1732-1738, June 2007”, wherein a parallel LC resonant circuit is utilized to achieve a decoupling function between two antennas. A parallel LC resonant circuit could be constructed by a capacitor, formed by a plurality of slots 23 embedded in the ground plane 20, and an inductance is formed by the vertical thin trace 24 between the slots 23. When the antennas 21, 22 operate with the resonance frequency, the parallel LC resonant circuit forms an open circuit, thus the current flowing from antenna 21 to antenna 22 can be blocked and the coupling between the antennas 21 and 22 is reduced to achieve an effectively higher isolation. However, the occupied area of proposed architecture is too large. In practical application, a complete area of the ground plane will not be added to this design, so this design does not make a substantial contribution to the reduction of size of the components.